Different person, but lately I’ve felt like mental TF could be caused through the same way as your option for cultural TF. It’s been shown that mental skills degrade if you use them less… and if you’re around idiots, you’re not going to use those skills as much in your daily life. It might even be a force from people around whoever’s being changed, either through a pressure not to go above everyone else’s heads in conversation or a direct vocalization to stop “acting so damn better than us.”

The line between mental and culture TF is a very very blurred one. You could probably go so far as to lump them together, but I do draw a distinction between them. Namely, cultural TF can only occur within the context of an Other–without some sort of cultural context for the shift to occur in, cultural TFs would make no sense at all. Mental TF, on the other hand, can occur without that cultural context. 

To illustrate–a character can become dumber without having another character in the story. However, a character cannot become a redneck without the larger world containing “rednecks,” whether that character encounters them or not. That social context makes for different kinds of change than a simple mental change without context.

However, cultural situations, changes and MacGuffins can certainly affect mental states and abilities. They can also affect physical changes (e.g. living with a group of rednecks who drink to excess gives a character a beer belly) but I wouldn’t want to blur that distinction.

So, in summation, your point it correct, cultural TF MacGuffins can also create mental change, but it would be good to separate them out anyway–at least from the authorial perspective–in order to keep track of what’s going on with your characters in the story, if that makes sense.